Forschungsprojekte

We were able to demonstrate the strongly anisotropic absorption behavior of Co-MOF-74 rod like crystals with a length of several hundred micrometers illuminated by polarized light. Afterwards Co-MOF-74 has been evaluated for selective gas sensing. Several gases (CO2, propene, propane, Ar, MeOH, H2O) can be detected and distinguished by Co-MOF-74 due to their interactions with the Co2+- centers.

It has been recognized that microcirculation plays an important role in pathogenesis of many diseases. Understand-ing and regulation of microvasculature are urgently needed for developing effective therapeutic strategies. Howev-er, suitable models allowing in depth biomedical research of microcirculation are missing. Most of the research is performed with the use of animal models. The main aim of the project is to develop human cells-based microvessel microfluidic model (HZ-MMM). Vessels are grown from microvascular endothelial cells (EC) and accompanying cells in a microfluidic device by the process of angiogenesis. The model is adjusted for applications in basic research and drug development.

we have measured the non-equilibrium spin noise of a homogeneously broadened single quantum dots in a microcavity. The measurements in combination with a theoretical analysis beyond the fluctuation-dissipation theorem reveal the spin dynamics in the ground and the excited state of the strongly driven artificial atom which is potentially useful for spin-photon interfacing.

an UiO-67 membrane was prepared and characterized for the first time in terms of its H2 purification properties. Further, a light switchable guest molecule was introduced into the MOF network, which could be used to switch the gas transport of CO2 by light over the permeance of H2, resulting in selectivity changes. Thereby, an easy and cheap way of making a switchable membrane was achieved and functionally tested.

We demonstrate the strong suppression of shot noise in a single-electron transistor using an exclusively electronic closed-loop feedback. The occurrence of shot-noise, due to the random emission of electrons with the quantized charge e-, was first postulated in vacuum diodes by W. Schottky in 1918 and is becoming the dominant source of noise in present-day mesoscopic conductors. Our technique is analog to the generation of squeezed light in quantum optics, using in-loop photo detection.

In this work we present the successful integration of two plasmonic semiconductor systems into the nanoporous MOF type ZIF 8. Both systems are potentially interesting for sensory application in which the ZIF network is size discriminating the access to the LSPR particles and can be either used for optical sensing of redox active substances or for simply sensing changes in the dielectric surrounding.

Hydrogen production by catalytic steam reforming of renewable hydrocarbons like bio-methane or bio-ethanol has become an attractive goal of sustainable chemistry. Side reactions as in ethanol steam re-forming decrease the hydrogen selectivity. A low-temperature catalytic membrane reactor with a hydrogen-selective membrane is expected to solve this problem. Three different carbon membranes are investigated with respect to their performance to extract hydrogen selectively.

A synthetic strategy to obtain highly porous aerogels from quasi 2D 5 ML thick CdSe and CdSe/CdS NPLs is presented. The aerogels partially exhibit the quantum confinement properties of their initial building blocks with a highest absolute quantum yield of 10.3%. The aerogels solely exhibit (111) as the exposed crystal facet. This type of extremely lightweight aerogels with high porosities and BET specific surface areas are promising for future applications for e.g., facet dependent catalytic reactions or in sensing chemicals.

We present a novel approach for synthesizing aerogels by shock-freezing colloidal nanoparticle in liquid nitrogen and subse-quent freeze drying. With this simple method it is possible to assemble nanoparticle into macroscopic voluminous monoliths, while retaining most of their properties such as size, shape or optical properties. In comparison to state of the art techniques it is a lot faster and easier to handle. This procedure might bridge the gap for scaled-up production and might enable industrial applications.

Hydrogels and aerogels from CdSe/CdS nanorods have been fabricated. By precisely controlling the gelation process, gels with high photoluminescence quantum yield and ultra-long exciton lifetime can be obtained. Thus, this type of assemblies represents a very promising way to fabricate materials that present new or improved characteristics with respect to both the colloidal solution and the bulk.

We have characterized in this joint collaboration Graphene nanoribbons, grown selectively on the sidewalls of SiC mesa. The identification of charge neutrality, monolayer thickness as well as the zig-zag orientation is important and a prerequsiste for the ballisitic transport behavior.

A continuous flow protocol for the oxidation of alcohols to aldehydes and ketones, respectively, using oxygen gas or atmospheric air is reported. The key features of this work are gold nanoparticles that are attached to the surface of nanostructured core shell particles composed of an Fe3O4-containing core and a silica shell. These nanostructured particles exert superparamagnetic properties and thus inductively heat up in an external oscillating electromagnetic field, conditions under which the gold cata-lyst is able to perform these oxidation reactions.

Microfabrication holds great promise for a new class of atomic and molecular quantum systems based on scalable and compact trapping structures. These systems have found applications both in quantum information science, novel types of quantum sensors and precision experiments. We design, fabricate, characterize and operate microfabricated neutral atom and ion chip-scale traps both at LNQE and in the PTB cleanroom facility.

In this work, we have grown Au, Pd, and Pt metal domains site-selectively on quasi 2D CdSe nanoplatelets of 5 monolayer thickness. Au and Pd domains are found mainly at the corner and at the shorter edges of the NPLs, whereas the Pt domains are all around the edges of the nanoplatelets. The different morphologies obtained for different metals are attributed to the type of metal precursor and to the varied reaction parameters.

The electronic properties of bilayer graphene strongly depend on relative orientation of the two atomic lattices. Whereas Bernal-stacked graphene is most commonly studied, a rotational mismatch between layers opens up a whole new field of rich physics, especially at small interlayer twist. We investigate magnetotransport measurements on twisted graphene bilayers, prepared by folding of single layers. These reveal a strong dependence on the twist angle, which can be estimated by means of sample geometry.

A continuous flow protocol for the oxidation of alcohols to aldehydes and ketones, respectively, using oxygen gas or atmospheric air is reported. The key features of this work are gold nanoparticles that are attached to the surface of nanostructured core shell particles composed of an Fe3O4-containing core and a silica shell. These nanostructured particles exert superparamagnetic properties and thus inductively heat up in an external oscillating electromagnetic field, conditions under which the gold catalyst is able to perform these oxidation reactions.

Despite of the numerous investigations of poly-Si/c-Si junctions performed in bipolar microelectronics, the current transport mechanism across these types of junctions is still not fully understood. Existing models assuming a tunneling of charge carriers through an interfacial oxide between the poly-Si and the c-Si fail to describe consistently the behavior of junctions with n-doped and p-doped poly-Si. Therefore, we have developed an alternative, rather simple analytical model assuming a dominant current flow through pinholes in the interfacial oxide.

We have shown the first synthetic pathway towards CdSe@CdS/ZnS nanorods with a sharp boundary between the CdS and the ZnS parts of the rods. The concept of sequential cation exchange reactions has been herewith extended to another interesting material combination which was not directly accessible. These new types of nanorods are promising candidates for applications where a good electronic insulation of the CdSe core is necessary and where the nanorods are contacted end-on.

We propose an approach for the magnetic bead-based capture and release of metallic nanoparticles of the platinum group, which can be interesting for many small-scale synthesis reactions e.g. in the area of fine chemical production. The application of magnetic beads for the capture and manipulation of metallic nanoparticles has hardly been under investigation so far. The development of a microfluidic magnetic bead-based separation system might allow for a re-use of the Pd catalyst, which would be of high industrial impact. The investigations described here can be used for both, Pd and Pt particles featuring similar chemical properties.

One of the key parameter for solar cells is the surface recombination velocity of the charge carriers which limits the efficiency of photovoltaic devices. Therefore, a homogenous surface passivation with excellent electronic properties is demanding for future applications. There are two complementary contributions for a reduction in the surface recombination velocity: a reduction in the density of electronic surface states (‘chemical passivation’) and, secondly, a reduction in the electron or hole concentration near the surface, e.g., by a band bending in Si-surface toward the interface (‘field-effect passivation’). Al2O3 films grown by atomic layer deposition (ALD) on crystalline silicon (c-Si) were shown to exhibit both contributions due to a well-defined interface structure and a high negative fixed charge density localized with in 1nm of the interface. In this joint project the chemical and electrical properties of passivation films have been studied by means of X-ray photoelectron spectroscopy (XPS) and capacitance-voltage (CV) analysis, respectively.